1. Field of the Invention
The present invention generally relates to an apparatus for processing the surface of a substrate to be processed, and more particularly to processing a semiconductor wafer or a glass substrate through coating or cleaning.
2. Description of the Related Art
During fabrication of a semiconductor device, spin coating is typically performed in photolithography. The spin coating technique is the process of coating a high-viscosity solution like photoresist onto the surface of a substrate to be processed such as a wafer and forming a high-viscosity resin film on the substrate by spinning the coated substrate.
A substrate surface processing apparatus, which carries out the spin coating, controls the thickness of the photoresist layer by adjusting the spinning speed of the substrate and forms the thin film by spinning the wafer at high speed. The substrate surface processing apparatus also cleans the substrate by coating a cleaning solution onto the substrate.
FIG. 1 is a sectional view illustrating major parts of a conventional substrate surface processing apparatus. Referring to FIG. 1, the substrate surface processing apparatus includes a spin chuck 310 for holding a substrate W thereon by suctioning, spinning, and moving up and down the substrate W, and upper and lower bowls 110 and 210 surrounding the spin chuck 310, for receiving a photoresist solution. An air outlet 510 is disposed under the lower bowl 210, for exhausting air from the bowls 110 and 210. The air outlet 510 is connected to an air pump (not shown) and air is forcedly exhausted from the bowls 110 and 210 through the air outlet 510 by the operation of the air pump. The substrate surface processing apparatus is further provided with a photoresist solution tank (not shown) and a supply nozzle (not shown), for supplying the photoresist solution onto the substrate W.
Because the substrate W is spun at a high speed (e.g. 1000 to 4000 rpm), a large amount of the photoresist solution is splashed out of the substrate W in the substrate surface processing apparatus. To prevent scattered fine particles of the photoresist solution from moving up to the upper bowl 110 and contaminating other devices, air is exhausted from the bowls 110 and 210 through the air outlet 510. The lower bowl 210 is shaped like a cup at its lower portion in order to receive the splashed photoresist solution.
As illustrated in FIG. 1, however, the substrate surface processing apparatus still faces the problem of particle contamination because photoresist particles bump against the upper bowl 110 and drop down onto the substrate W or fine photoresist particles fall onto the substrate W along air flows 411 and 413 that reflow from the inner walls of the bowls 110 and 210 during photoresist coating on the substrate W. Moreover, the splashed photoresist solution or particles stick to a lower end portion of the upper bowl 110, causing a so-called icicle phenomenon. Therefore, much time is taken to clean the bowls 110 and 210 regularly. In the context, studies are being conducted to provide an upper bowl flow control protrusion 110a at the lower end portion of the upper bowl 110 in order to appropriately control the air flows 411 and 412.
FIG. 2 is a sectional view illustrating another conventional substrate surface processing apparatus, disclosed in Japanese Laid-Open Patent No. 2001-189266.
Referring to FIG. 2, the substrate surface processing apparatus includes a spin chuck 10 for spinning a wafer W thereon, and a supply nozzle 11, a supply pipe 12, a control valve 13, and a photoresist solution tank 14, for depositing a photo-resist layer on the wafer W. The substrate surface processing apparatus is further provided with a holder 17, a Z-direction mover 16, and a Y-direction mover 15, for moving the supply nozzle 11 in the directions of Z and Y. A cup 24 surrounds the spin chuck 10 to receive the photo-resist solution splashed out due to the spinning of the wafer W, and an air flow control plate 25 of the substrate surface processing apparatus is installed at the gap between the wafer W and the inner circumferential surface of the cup 24. At the bottom of the cup 24 is disposed an air outlet 30. The air outlet 30 is connected to a pump 32 via a control valve 31. Air is forcedly exhausted from the cup 24 through the air outlet 30 by the pump 32. The resultant negative pressure occurred inside the cup 24 creates a downstream air flow D from up to down in the cup 24. The downstream air flow D flows to the bottom of the cup 24 through exhaust holes of the air flow control plate 25.
The substrate surface processing apparatus is provided with the air flow control plate 25 to prevent a rapid increase in the thickness of a photoresist layer caused by a change in the air flow around the wafer W. Since the distance between the edge of the wafer W and the air flow control plate 25 in the surface processing apparatus is relatively narrow and extra photoresist splashes over the air flow control plate 25, the photoresist solution may be still splashed back, an icicle may be still generated, and air may reflow around the air flow control plate 25.
FIG. 3 is a sectional view illustrating a third conventional substrate surface processing apparatus, disclosed in Korean Utility Model Registration No. 2002-22598. The substrate surface processing device includes a spin chuck 1 for spinning a wafer W thereon, a nozzle 52 for providing photoresist solution to the wafer W, and a cup-shaped case 40. A plurality of annular splash-back preventing portions 41, 42 and 43 are formed around the inner surface of the case 40 at different inclination angles, to thereby prevent the photoresist solution from splashing from the wafer W, bumping against the wall of the case 40, and then returning to the wafer W. However, the structure of the substrate surface processing apparatus also has limitations in its effectiveness to remove particle contamination, which is encountered as photoresist particles drop onto the wafer W along the air flow within the case 40.
Additionally, to prevent the photoresist solution from scattering or splashing back, a mesh or a net is provided within a bowl, a cover is provided on a bowl, or another air inlet is provided over a bowl so that a downstream air flow is formed which moves down along the inner bowl of the bowl and, in turn, extra photoresist solution may not stick to the inner wall of the bowl. Despite the above proposals, the particle contamination of the substrate is yet to be solved.